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March 20, 2024 13:59
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linuxcnc max_velocity settings
This guide explains how various max_velocity
settings interact in LinuxCNC's .ini
configuration file, focusing on the [traj]
, [axis]
, and [joint]
sections, and their relationship with stepgen_maxvel
.
max_velocity
in Different Sections:
-
[traj]
Section:DEFAULT_LINEAR_VELOCITY
(orDEFAULT_VELOCITY
): Sets the default speed for linear jogs (straight-line movements) in machine units per second (default starting point for manual jogging).MAX_LINEAR_VELOCITY
: Defines the absolute maximum velocity for any linear movement (including jogs, G-code commands, and coordinated moves). This acts as a hard limit for safety.
-
[axis]
Section:MAX_VELOCITY
: Specifies the maximum velocity for a specific axis, also in machine units per second. Allows tailoring speed for each axis based on its limitations. This value should generally be lower than or equal to the globalMAX_LINEAR_VELOCITY
in[traj]
.
-
[joint]
Section (Rotary Axes):MAX_VELOCITY
: Similar to the axis section, this sets the maximum velocity for a rotary axis, again in units per second (e.g., degrees or radians per second).
Interaction with stepgen_maxvel
:
stepgen_maxvel
(found in[EMC]
) is an internal parameter for the step generator used by stepper motors. It defines the maximum step rate the step generator can handle (typically in encoder steps per second).
Relationship Between max_velocity
and stepgen_maxvel
:
- LinuxCNC uses
max_velocity
values and the machine's physical properties to calculate the required step rate for each axis. - Internally, it converts the desired
max_velocity
to steps per second and compares it tostepgen_maxvel
. - If the calculated step rate exceeds
stepgen_maxvel
, LinuxCNC reducesmax_velocity
to a level that doesn't overload the step generator, potentially sacrificing some speed for stability.
Key Points:
MAX_LINEAR_VELOCITY
in[traj]
sets the overall limit for linear movements.MAX_VELOCITY
in[axis]
allows for axis-specific speed adjustments.MAX_VELOCITY
in[joint]
is for rotary axes, expressed in appropriate units.stepgen_maxvel
is an internal limit for stepper motors.- LinuxCNC ensures
max_velocity
doesn't exceed stepper motor capabilities.
Additional Considerations:
- Actual achieved velocity can be further limited by factors like acceleration settings, machine dynamics, and real-time constraints.
- It's generally recommended to keep
max_velocity
values conservative for smoother operation and reduced wear. - Adjust these settings cautiously, starting with lower values and gradually increasing them while observing machine behavior.
By understanding these concepts, you can effectively configure your LinuxCNC system for optimal performance and safety within your hardware's constraints.
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